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crandmck
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Mar 9, 2026
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We should update this PR depending on how the comments on contentauth/c2pa-rs#1900 are resolved. |
docs/embeddable-api.md
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| Use this workflow with MP4 and other BMFF formats, which always require a placeholder. The `prefer_box_hash` setting has no effect on BMFF formats: they always use `BmffHash` regardless of the setting. No special Builder settings are required as the SDK selects `BmffHash` automatically based on the format. | ||
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| BMFF containers (ISO Base Media File Format) store media data in `mdat` (media data) boxes, which hold the raw audio, video, and other media samples. These `mdat` boxes can be very large, making it expensive to re-read the entire file to compute a hash after signing. The SDK addresses this with a Merkle tree structure in the `BmffHash` assertion: it divides `mdat` content into fixed-size chunks and computes a hash for each chunk (a "leaf" in the tree). These leaf hashes are combined into a Merkle root hash that covers the entire `mdat` content. The `placeholder()` method pre-allocates slots in the `BmffHash` assertion for these Merkle leaf hashes, sized according to the `core.merkle_tree_chunk_size_in_kb` setting. This pre-allocation is necessary because the final manifest must be exactly the same size as the placeholder for in-place patching to work. |
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This section is no longer correct. See these:
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Ack, will update accordingly but will take a few cycles to do so.
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@mauricefisher64 Are additional bindings needed?
Eg. c2pa_builder_set_fixed_size_merkle & friends are for the streaming APIs, so we don't need them here now, and can ignore them in those docs?
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